private void kasirToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (frmKasir == null)
     {
         frmKasir             = new FormMasterKasir();
         frmKasir.FormClosed += new FormClosedEventHandler(frmKasir_fromClosed);
         frmKasir.ShowDialog();
     }
     else
     {
         frmKasir.Activate();
     }
 }
 void frmKasir_fromClosed(object sender, FormClosedEventArgs e)
 {
     frmKasir = null;
 }